1. Technical Field
The present invention relates to a hologram element, an illumination device, a projector, and a method of manufacturing a hologram element and more particularly, to a technique of a hologram element used in an illumination device of a projector.
2. Related Art
In recent years, a projector is becoming smaller in size. A spatial light modulation device, for example, a liquid crystal display device is also becoming smaller as a projector is becoming smaller. In the case of a transmissive liquid crystal display device that transmits light, a rate of a black matrix serving as a light shielding portion between pixels increases as the liquid crystal display device becomes smaller. As a result, an aperture ratio decreases. On the other hand, in the case of a reflective liquid crystal display device that reflects light, a control line for every pixel is disposed below a reflection electrode. Accordingly, it is possible to make a gap between pixels extremely small. A decrease in opening ratio can be reduced by making the gap between pixels small. In addition, in the case of using a reflective liquid crystal display device, an optical system may also be reduced in size by adopting a configuration in which light is emitted by using the same optical path as light incident on the reflective liquid crystal display device. From those described above, it can be said that the reflective liquid crystal display device is suitable for miniaturization of a projector. A technique of a projector using a reflective liquid crystal display device is proposed in JP-A-2006-84820, for example.
A technique of using a laser light source as a light source of a projector has been recently proposed. As compared with an ultra-high pressure mercury lamp (UHP lamp) that has been used as a light source of a projector in the related art, the laser light source is advantageous in high color reproducibility, instant lighting, a long life, and the like. A hologram element can be used in an illumination device using a laser light source. In the hologram element, shaping and enlargement of an illuminated region and equalization of the light amount distribution in the illuminated region may be performed simultaneously by diffracting a laser beam. The hologram element can correctly perform shaping of an illuminated region, equalization of the light amount distribution in the illuminated region uniform, and the like by adopting a configuration corresponding to the wavelength of diffracted light. In the case of displaying an image with a plurality of color light components, a hologram element for every color light component is used to achieve reliable optical performance.
In the case of combining a hologram element and a reflective liquid crystal display device, it is difficult to adopt a configuration in which light is emitted by using the same optical path as light incident on the reflective liquid crystal display device, and an optical path from a laser light source to the reflective liquid crystal display device is required for every color light component. Since an optical path from the laser light source to the reflective liquid crystal display device is required for every color light component, it is difficult to realize a compact optical system. As described above, in the known techniques, there is a problem that satisfactory optical performance with respect to light components in a plurality of wavelength regions and miniaturization of a structure where a hologram element is provided are difficult to be compatible with each other.